The present invention relates to Passive LCR (Inductor, Capacitor, Resistor), or simply LC, sensors. These sensors are widely used in the medical, industrial, military, and commercial applications. These passive sensors respond to various stimuli. These stimuli are often in the form of specific pulses, multiple pulses of that specific frequency, various pulses at different intervals and frequencies, a “white noise” consisting of a pseurandom signal, a Carrier Wave (CW) combined with “white noise”, a combination of AM or PM frequency, or a Carrier Wave transmitted at a specific or variable frequencies. Each of these stimuli is designed to result in a different response from the Passive LCR sensor. The capacity to accept multiple signals from disparate sources greatly enhances the features and functions of these passive sensors. The enhancements include but are not limited to: greater range, greater detection, greater operation efficiency, better and more effective communication with the devices that measure the sensors.
There are several prior art attempts related to sensors and circuits, where such attempts are detailed in the following U.S. patents:
a.) U.S. Pat. No. 4,265,252 to Chubbuck teaches an implantable transensor device containing a passive RF resonant circuit having a natural frequency influenced by the pressure of the sensor's environment in a body cavity of a living entity. The circuit of the transensor includes an inductor and a capacitor, at least one of which varies in value in direct relation to variation of environmental pressure to change the resonant frequency of the circuit. The circuit can be externally interrogated to determine the resonant frequency thereof at any point in time by the imposition thereon of swept frequency electromagnetic radiation provided by a monitoring device which determines when some of the radiation is absorbed as a result of the frequency of the radiation being the same as the resonant frequency of the transensor circuit. An imposed relationship exists between the sensed environmental pressure, and the reactance of the reactive components of the circuit. A natural relationship exists between pressure sensitive reactance, and the resonant frequency of the circuit. As a result, an increase in environmental pressure causes a corresponding increase in frequency and a decrease in environmental pressure causes a decrease in frequency.
b.) U.S. Pat. No. 5,619,997 to Kaplan teaches a passive sensor system utilizing ultrasonic energy is disclosed. The passive sensor system includes at least one ultrasonically vibratable sensor and an ultrasonic activation and detection system. The sensor has at least one vibration frequency which is a function of a physical variable to be sensed. The ultrasonic activation and detection system excites the sensor and detects the vibration frequency from which it determines a value of the physical variable. The sensor includes a housing, a membrane which is attached to the housing and which is responsive to the physical variable, a vibratable beam attached to the housing at one end and a coupler, attached to the membrane and to a small portion of the vibratable beam, which bends the vibratable beam in response to movement of the membrane.
c.) U.S. Pat. No. 6,744,174 to Paden, et al. is a frequency stability analysis and design method for frequency robust resonators, such as MEMS resonators, is presented. The frequency characteristics of a laterally vibrating resonator are analyzed. With the fabrication error on the sidewall of the structure being considered, the first and second order frequency sensitivities to the fabrication error are derived. A relationship between the proof mass area and perimeter, and the beam width, is developed for single material structures, which expresses that the proof mass perimeter times the beam width should equal six times the area of the proof mass. Design examples are given for the single material and multi-layer structures. The results and principles presented in the paper can be used to analyze and design other MEMS resonators.
d.) U.S. Pat. No. 6,461,301 to Smith relates to a resonance based pressure transducer system, insertable into a living body for the in vivo measurement of pressure. It comprises a pressure sensor (2) having a mechanical resonator (16), the resonance frequency of which is pressure dependent; and a source of ultrasonic energy (4). The sensor (2) is mechanically coupled to said source (4) of ultrasonic energy, and the sensor and the source of ultrasonic energy are provided on a common, elongated member (6) at the distal end thereof. A system for pressure measurement comprises an AC power supply, a resonance based pressure transducer system, and a control unit for controlling the supply mode of the AC power, and for analyzing a resonance signal emitted from the resonance based pressure transducer system.
e.) U.S. Pat. No. 5,339,051 to Koehler, et al. discloses a micro-miniature resonator-oscillator. Due to the miniaturization of the resonator-oscillator, oscillation frequencies of one MHz and higher are utilized. A thickness-mode quartz resonator housed in a micro-machined silicon package and operated as a “telemetered sensor beacon” that is, a digital, self-powered, remote, parameter measuring-transmitter in the FM-band. The resonator design uses trapped energy principles and temperature dependence methodology through crystal orientation control, with operation in the 20-100 MHz range. High volume batch-processing manufacturing is utilized, with package and resonator assembly at the wafer level. Unique design features include squeeze-film damping for robust vibration and shock performance, capacitive coupling through micro-machined diaphragms allowing resonator excitation at the package exterior, circuit integration and extremely small (0.1 in. square) dimensioning. A family of micro-miniature sensor beacons is also disclosed with widespread applications as biomedical sensors, vehicle status monitors and high-volume animal identification and health sensors. The sensor family allows measurement of temperatures, chemicals, acceleration and pressure. A microphone and clock realization is also available.
f.) U.S. Pat. No. 6,111,520 to Allen, et al teaches that several sensors are provided for determining one of a number of physical properties including pressure, temperature, and other physical conditions. In general, the sensors feature a resonant circuit with an inductor coil which is electromagnetically coupled to a transmitting antenna. When an excitation signal is applied to the antenna, a current is induced in the sensor circuit. This current oscillates at the resonant frequency of the sensor circuit. The resonant frequency and bandwidth of the sensor circuit is determined using an impedance analyzer, a transmitting and receiving antenna system, or a chirp interrogation system. The resonant frequency may further be determined using a simple analog circuit with a transmitter. The sensors are constructed so that either the resonant frequency or bandwidth of the sensor circuit, or both, are made to depend upon the physical properties such as pressure, temperature, presence of a chemical species, or other condition of a specific environment. The physical properties are calculated from the resonant frequency and bandwidth determined.
The manner by which the present invention increases the range of the sensor increases the means and number of communication methods increases the sensitivity of detection, and increases the reliability of communications all of which will become more apparent in the description which follows, especially in conjunction with the accompanying drawings.